JP3190292B2 - Detoxification method of sludge settled in electrolysis tank for impurity recovery in chromium plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detoxifying sludge containing harmful substances which is produced in a plating plant or the like in a large amount.

[0002]

2. Description of the Related Art At present, treatment means for a chromium plating solution, a chromium plating waste solution and the like which are performed in a plating factory are roughly classified into the following three types. 1. After hexavalent chromium contained in the chromium-based wastewater is reduced to trivalent chromium with a reducing agent, it is precipitated and separated as chromium hydroxide with an alkaline agent, and the supernatant water is discharged as treated water through outflow control. 2. The chromium-based wastewater is ion-exchanged with a free base type strong base anion exchange resin and recovered as trivalent chromic acid. In the treatment of chromium wastewater, it is necessary to control the upper limit of the concentration of chromic acid and desorb a strong base anion exchange resin.The pH is adjusted, hexavalent chromium is reduced to trivalent chromium, And sedimentation separation as chromium hydroxide. 3. It is reused as a chromium plating solution in an impurity recovery electrolysis tank and precipitates metal ions of impurities as iron hydroxide. The first and second chromium hydroxides and the third iron hydroxide are both harmful toxic substances. In any case, a reduction treatment and a neutralization treatment are performed, and the sludge is treated by a treatment method (elution of hexavalent chromium). At present, they are buried in the ground after being treated so that they do not correspond to poisons and deleterious substances specified in the industrial waste leaching landfill amount of 1.5 mg / l or less. 3 above
The second iron hydroxide periodically collects the chromium plating solution (specifically, chrome plating waste solution that is periodically replaced) in the chrome plating chamber for quality control, and removes the solid suspension contained in the filter. After filtering and separating suspended suspended substances, metal ions such as iron, copper and zinc contained in the chromium plating waste liquid and chromium are separated in an impurity recovery electrolysis tank and reused as a plating solution. Japanese Patent Application No. 7-327367 (Japanese Unexamined Patent Application Publication No. 9-165699) filed by a person
(Title of Invention) Chrome plating solution in chrome plating,
Chromium plating waste liquid, Chromic acid cleaning liquid in the closed recycling system for chromic acid washing water), Chromic plating waste liquid, and Chromic acid washing water are collected in a mixed solution, and iron, copper, and zinc contained in the mixed solution are collected. Similarly, when metal ions such as chromium are passed through a filter, they are separated in an impurity recovery electrolysis tank and reused as a plating solution. However, at present, the elution amount of hexavalent chromium can be reduced only to the extent that the elution amount of hexavalent chromium specified in the waste landfill standard is 1.5 mg / l or less. There's a problem. Besides, reduction treatment,
During the neutralization treatment, not only are various costs such as equipment costs, chemicals for treatment, and pollution treatment costs (sludge treatment) expensive, but also require advanced technology in operation management, exceeding the management ability of small and medium-sized enterprises It has become a major factor in oppression.

[0003]

Therefore, the present applicant has filed a prior application for making the sludge harmless from Japanese Patent Application No. 8-102527.
No. proposes. This prior proposal is a method in which sludge separated in an impurity recovery electrolysis tank is washed with water, sludge precipitated by washing with water is dried, and calcined to render the sludge harmless. However, in the future proposal, since only a small amount of 10 g of sludge was to be inspected, no elution of hexavalent chromium was unexpectedly observed.
When it was fired again with sludge of 0 g or more and inspected, hexavalent chromium was eluted, and detoxification could not be established as reproducible.

[0004] The present invention has been made in view of the conventional circumstances, and an object thereof is to solve the above-mentioned problems of the present sludge treatment means, and to contain harmful substances generated in large quantities in plating plants and the like. It is to make sludge harmless with reproducibility by effectively utilizing a certain substance.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies on the detoxification of sludge to which hexavalent chromium has adhered.
The inventors have found that natural organic substances remove hexavalent chromium, and have reached the present invention. That is, the present invention provides metal ions such as iron, copper, and zinc contained in a chromium plating waste liquid, or a mixed solution of a chromium plating solution, a chromium plating waste solution, and chromic acid washing water.
The sludge separated from the chromium in the electrolytic recovery tank is taken out, washed with water, and the chromium generated by this washing is removed.
Separate the washing water containing munic acid from the sludge, dry the sludge precipitated by washing, add natural organic matter to the sludge, and reduce and calcine it to reuse the sludge
The point is to detoxify as much as possible . In addition, it is preferable to effectively use rice husks, of which 80% are treated as industrial wastes throughout the country as natural organic matter.

According to the above technical means, the following effects are obtained. The method of detoxifying the sludge precipitated in the chromium plating impurity recovery electrolysis tank is as follows. A natural organic substance is added to the hexavalent chromium-attached sludge, stirred and reduced and calcined. ) ₂ O _{3 and the} like became solids present in the form of ferrite, and elution of hexavalent chromium was not detected. The mechanism by which hexavalent chromium is not detected is unknown, but the hexavalent chromium adhering to the sludge before firing becomes a reducing agent during firing, and the phenolic polymer contained in natural organic matter that becomes an organic reductant becomes trivalent. It is presumed that it will be changed to chromium and then to iron oxide, ferric oxide, trivalent chromium, etc., which are safe complexes surrounding it. And
Solid materials containing ferrite, such as iron oxide, ferric oxide, and trivalent chromium, that are produced in the form of ferrite, have high quality as magnetic materials, such as magnetic tape, radio wave absorption plates that prevent radio interference, and thermoelectric conductivity. Utilizing its superior properties, it can be widely reused as a material for solar heat absorption, a pavement material in cold regions, a mixed material for road heating materials, a mixed material for fish reef materials, and the like.

[0007]

Next, an embodiment of the present invention will be described with reference to the drawings. In the present invention, the chromium plating solution, the chromium plating waste solution, and the mixed solution of the chromium plating waste solution and the chromic acid cleaning water in the closed recycling system process for the chromic acid cleaning water shown in FIGS. A method for detoxifying sludge (chromic acid containing iron hydroxide and trace amounts of hexavalent chromium and trivalent chromium) which is electrolyzed and recovered in the decomposition tank A will be described.

[0008] The closed recycling of the present embodiment
As shown in Fig. 1, the system is chromium plating required equipment such as recovery tank B, chrome plating tank C, filter D, impurity recovery electrolysis tank A, chromate mist recovery device E, chromate mist washing tower F, etc. And a filter D, a chromate mist collection device E, a chromate mist washing tower F, etc., in a collection tank B.
A chromium plating tank C is arranged above the recovery tank B, and the chromium plating solution, chrome plating waste liquid, chromic acid washing water, etc. are all collected in the recovery tank B so as not to flow out of the chrome plating chamber. is there.

The chromium plating tank C is a facility for applying chromium plating to an object to be plated. The chromium plating tank C is installed above the recovery tank B, and the chromium plating solution leaks out, or the chromium plating object c is pulled up to remove the chrome plating tank. Chromic acid water generated when shower water is washed on C can be collected in the collection tank B. Since chromium plating is performed by electrolysis, the anodes c1 and c1
Are arranged, and an object to be plated 100 is placed between the electrodes c1 and c1 to perform chrome plating.

The recovery tank B includes a chromium plating solution leaking from the chromium plating tank C, a chrome plating waste liquid exchanged from the chrome plating tank C for quality control, a chromic acid mist recovery device E described later, All of the chromic acid water, the chromic acid cleaning water, and the like from the mist cleaning tower F are collected.

The filter D is used for filtering and separating solid suspended and suspended substances (particle size: 1.7 to 7.0 μ) contained in the chromium plating solution, the chromium plating waste liquid, and the chromic acid washing water in the recovery tank B. Chromium plating solution, chromic acid washing water, chrome plating waste solution, etc. are sucked up from the recovery tank B by the suction pipe 1, and the solid suspended and suspended substance is filtered by the internal filter tube (not shown). , And is sent to the impurity recovery electrolysis tank A for removing impurities.

As shown in FIG. 2, the impurity recovery electrolysis tank A is for reducing impurities (metal ions such as iron, copper and zinc, trivalent chromium, etc.) and removing precipitates. As shown in FIG. 2, the tank 2 itself is formed as a double tank comprising an outer tank 12 and an inner tank 22, the outer tank 12 is lined with iron and a CFC sheet, and the inner tank 22 is made of a hard vinyl chloride resin. The inside of the inner tank 22 is divided into an anode chamber 42 and a cathode chamber 52 by a
It has + and-busbars at its upper part, and a lead alloy anode 62 and an iron cathode 72 are suspended from each busbar, and each is filled with a chromium plating solution (a solution obtained by filtering and separating a solid suspended and suspended substance), When the electrolysis is started, the three reactions proceed in parallel to generate a highly concentrated chromic acid (hexavalent chromium) regenerating solution with a small amount of impurities in the anode chamber 42.

That is, when electrolysis is started in the anode chamber 42 and the cathode chamber 52, electrodialysis of chromic acid from the cathode chamber 52 through the diaphragm 32 to the anode chamber 42 occurs, and dialysis of chromic acid is performed. At the same time, electrolytic oxidation (Cr ³⁺ → CrO ₃ ) of trivalent chromium (Cr ³⁺ ) to chromic acid proceeds in the anode chamber 42, and as a result, the chromic acid concentration in the anode chamber 42 increases and trivalent chromium decreases. Then, at the end of the electrolysis, a regenerating solution that can be used as it is as a chromium plating solution is obtained. On the other hand, in the cathode chamber 52 of the impurity recovery electrolysis tank A, chromic acid, which has been combined with iron, is reduced to form trivalent chromium by electrolysis of the chromium plating solution, and metal ions of impurities (iron,
Metal ions such as copper and zinc) separate from the complex compound and precipitate as sludge (iron hydroxide) X.

The chromic acid mist recovery device E is a dry type device, and a chromic acid mist k generated by oxygen and hydrogen generated when electrolysis of chromium plating is performed.
Has the purpose of collecting and liquefying it and transferring it to the collecting tank B.

As shown in FIGS. 3 and 4, the internal structure of the dry type chromic acid mist recovery device E is such that the chromic acid mist liquefied plate 3 having a portion at 45 degrees to the direction of the flow of the chromic acid mist is vertically oriented. When the chromic acid mist k collides with inertia and rotational force, it liquefies and adheres, flows through the liquefied plate 3 and is collected in the collecting groove 13, and becomes chromic acid liquid from the collecting liquid receiving tank 23. It flows out to the recovery tank B via the outflow pipe 33.
The chromic acid mist liquefied plate 3 has a U-shaped plate 43 at one end and a 45 ° inclined plate 53 at the other end, as shown in FIGS. , A U-shaped plate 43 at one end and a parallel plate 63 with the U-shaped plate 43 at the other end.
And the distance between the U-shaped plate portion 43 and the parallel plate portion 63 is 45
The second liquefied plate 3 ″ having the inclined plate portion 73, and the mist inside the device body such that each of the inclined plate portions 53 and 73 is at 45 degrees to the direction of the flow of cumuloic acid mist k. The same number of the inlet side part (chrome plating tank side part) 83 and the mist outlet side part (chromic acid mist washing tower side part) 93
The letter-shaped plate portions 43, 43 are arranged facing the mist outlet side.

The chromate mist cleaning tower F is a device for cleaning and removing the dry chromic acid mist and the chromic acid mist k which could not be liquefied by the recovery device E. A shower 4 is provided inside the tower body, and the shower 4 is provided. 4. Chromic acid exhaust gas concentration measurement inspection hole 14 was opened at the middle part of the duct above, and the inspection hole
An exhaust fan 24 is arranged above the exhaust fan 24, and an exhaust window 34 is opened above the exhaust fan 24.

When the exhaust fan 24 is operated in the chromate mist washing tower F, the chromate mist k, which cannot be liquefied by the dry chromic mist recovery device E, is sucked into the tower and is washed with washing water poured from the shower 4. It is washed and removed in the recovery tank B.

As described above, the chromium plating solution leaking from the chrome plating tank C and the chromic acid water and the chromic acid mist recovery device E generated when the object to be plated 100 is pulled up and washed with the shower 5 on the chromium plating tank C, All the chromic acid water and the chromic acid washing water from the chromic acid mist washing tower F are collected in the collecting tank B, and the mixed solution in the collecting tank B is filtered with the filter D to obtain the diaphragm type impurity collecting electrolysis tank A. To generate a regenerating solution that can be used as a chromium plating solution, and supply the regenerating solution to the chromium plating tank C.

In the detoxification method of the present invention, as shown in FIG. 5, a chromic acid solution containing mainly iron as impurities, copper and zinc is separated from an impurity recovery electrolysis tank (specifically, a cathode chamber of the tank) A. After being pumped up, the precipitated sludge (iron hydroxide) X is taken out to another recovery tank with a vacuum cleaner, distributed to a water washing tank, and repeatedly washed with water (agitated water washing). The rinsing water containing chromic acid is separately stored in a pit and can be reused as a chromic acid solution or the like for the cathode chamber of the impurity recovery electrolysis tank A. After washing with the stirring water, dehydration may be further performed by a centrifugal separator.

The water washing is preferably carried out until the amount of hexavalent chromium eluted from the sludge (iron hydroxide) becomes 0.2 g / l or less, and then the sludge X is dried and natural organic matter is reduced for reduction. In addition, reduction firing is performed thereafter.

As the drying means, air drying or forced drying can be individually and selectively employed. In consideration of the fact that the sludge X is a fine powder, if the air is naturally dried, the sludge X is packed in a packaging container (for example, a can, Others), dried at room temperature for a certain period of time (for example, about two weeks), and if forced drying, dry under no wind conditions (for example, spread the sludge X on the floor in the room and do not blow hot air. To warm the room and dry).

The sintering is carried out in an electric furnace or a porcelain ware kiln, with a chromium component (hexavalent chromium / trivalent chromium) adhering sludge 1000
g is used as an organic reducing agent, and chaff (natural organic matter) is added and stirred. When the amount of hexavalent chromium attached is 0.2 g / l, 30 (300 g) percent of rice husks are added in a weight ratio and stirred, and then fired at a reduction firing temperature of 900 degrees and a firing holding time of 240 minutes, elution of hexavalent chromium is detected. No elution of hexavalent chromium was detected even at a reduction firing temperature of 1000 ° C. and a firing holding time of 180 minutes. In addition, the amount of hexavalent chromium deposited is 0.1.
In the case of 1 g / l, the weight ratio is 15 (150 g) percent, and in the case of the same adhesion amount of 0.3 g / l, the weight ratio is 45 (45 g).
0g) percent, and in the case of the same adhesion amount of 0.4 g / l, the rice husks are added and stirred in an amount of 60 (600 g) percent by weight ratio, that is, the rice husks are weighted in proportion to the adhesion amount of hexavalent chromium. Added. As described above, the addition of a weight percent of rice hulls compatible with the attached amount of hexavalent chromium and stirring and firing at the reduction firing temperature and firing holding time, no elution of hexavalent chromium was detected in any pattern. .

The hexavalent chromium adhering to the sludge X before firing is converted into trivalent chromium as a reducing agent during the firing of the phenolic polymer contained in natural organic matter (rice husk), and is a safe wrapping material. Complex iron oxide, ferric oxide,
It becomes trivalent chromium or the like, which is presumed to be harmless.

When washing with water is carried out until the amount of hexavalent chromium eluted is 0.2 g / l or less, a large amount of washing water containing hexavalent chromium is transferred to the washing water for the plating object and the chromium plating tank. Not only can it be effectively used as replenishing water, but when the concentration is high, it can be recovered once in the recovery tank B and used as a chromic acid solution for the cathode chamber of the impurity recovery electrolysis tank A via the filter D.

Although not shown in the present embodiment, a plating solution in a chrome plating chamber (specifically, a chrome plating waste solution which is periodically replaced (hereinafter referred to as a chrome plating waste solution)) is periodically used for quality control. And then remove the iron, copper, zinc and other metal ions and chromium contained in the recovered chromium plating wastewater through a filter to remove solid suspended suspended substances, and then use an impurity recovery electrolysis tank. The present invention can be equally applied to a method for detoxifying sludge generated when separated and reused as a plating solution.

[0026]

As described above, according to the present invention, sludge deposited in the electrolysis tank for recovering chromium plating impurities can be rendered harmless. Solid materials in which the generated iron oxide, ferric oxide, trivalent chromium (Fe.Cr) ₂ O _3, etc. are present in the form of ferrite are high quality magnetic materials, and magnetic tapes and radio wave absorption for preventing radio interference. It can be used for various purposes such as materials for solar heat absorption, pavement materials in cold regions, mixed materials for road heating materials, mixed materials for fish reef materials, etc. Is excellent. In addition, rice husks that are disposed of as industrial waste at a cost of as much as 80% nationwide can be effectively used, which is a great deal.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a closed recycling system incorporating an impurity recovery electrolysis tank used in the sludge detoxification method of the present invention.

FIG. 2 is a schematic explanatory view of the inside of an impurity recovery electrolysis tank.

FIG. 3 is an internal explanatory plan view of the chromate mist collection device.

FIG. 4 is a sectional view taken along line (4)-(4) in FIG. 3;

FIG. 5 is a process diagram of the sludge detoxification method of the present invention.

[Explanation of symbols]

 A: Impurity recovery electrolysis tank

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C02F 11/00-11/20

Claims (2)

(57) [Claims] 1. Metal ions such as iron, copper, zinc and chromium contained in a chromium plating waste liquid or a mixed liquid of a chromium plating liquid, a chromium plating waste liquid and a chromic acid washing water are separated in an impurity recovery electrolysis tank. Take out the sludge, wash with water, and wash water containing chromic acid generated by this washing
And sludge separately, drying the sludge precipitated by washing with water, adding natural organic matter to the sludge, and reducing and firing the sludge, thereby rendering the sludge harmless so that it can be reused. Detoxification method of sludge settled in electrolysis tank for recovery of impurities in plating. 2. The method according to claim 1, wherein the natural organic matter is rice hulls.